Police tracked that call to phone booth in the 300 block of Columbus Avenue and a lockdown was immediately issued as law enforcement from several agencies descended upon the university and began going room to room to search of the campus.

Police said yesterday that they believe the call was a hoax, but they took it seriously and have captured surveillance images from the area.

"We don't have the luxury of going on a hunch, so we are gong to run this down to ground all the way," New Haven Police Chief Dean Esserman said.

Police spoke with several people who were not sure whether the person they said they saw with a gun was a citizen or a police officer.

Today, police said they believe a witness who reported seeing a man with a gun near the Lindsley-Chittenden Hall on High Street after the alert went out might have in fact spotted a law enforcement officer who was responding to the emergency.

Police also said there were reports from people on campus seeing someone on a roof or someone, but it turned out to be someone who was smoking a cigarette.

"Nobody has been hurt, nobody has been found, but the day is hardly over," Esserman said. "Because, until we are satisfied that perhaps a police officer was mistakenly seen with a gun, and not a civilian seen with a gun, we are going to err on the side of caution. I want to repeat -- nobody has been shot. Nobody has been hurt. Nobody has been apprehended with a gun. ... But in this day and age, when there is a call, it behooves us to over-react and not under-react."

The caller who triggered the massive police response did not identify himself and only stayed on the phone with dispatchers for a few seconds before hanging up, David Hartman, of the New Haven police department said.

Immediately after receiving the call, Yale University ordered a shelter-in-place/lock-down order and state police, the FBI, ATF and other federal agents joined Yale and New Haven police in the investigation.

Esserman said during a news conference yesterday afternoon that police have tracked down the call and they are tracking down the person who made it.

"I'm not, and Chief Higgins is not going to walk away and go home tonight until everybody we're responsible for keeping safe is safe," Esserman said yesterday. "And thought it is starting to tilt in the direction of an innocent mistake, it started with a purposeful and malicious call and the New Haven Police are going to track down the person who made that call, we're going to find the person who made that call, we're going to put handcuffs on the person who made that call."

One Yale student said she was the only person in her suite when the lockdown was issued. For four hours, she remained inside while her father waited outside to take her home for the Thanksgiving break.

After police knocked on the door and searched her room, she was allowed to leave.

This is a situation that played itself out over and over again today as police do a room to room search that started with the residential college areas.

"When (police) knock on your door, a Yale Police Officer will slip their Yale ID under the door. Please cooperate. In some cases, Police may use keys, but they will identify themselves. Shelter in Place continues," an alert the university issued at 1:45 p.m. said.